Methods for immobilizing anti-thrombogenic material onto a medical device or into a coating thereon

ABSTRACT

The present invention is directed to a medical device having a polymerized base coat layer for the immobilization of an anti-thrombogenic material, such as heparin, thereon. The binding coat layer is comprised of various chemically functional groups which are stable and allow for the immobilization of the anti-thrombogenic material thereto. Methods for immobilizing the anti-thrombogenic material within the base coat layer posited on a surface of the medical device are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/918,365, filed Jul. 30, 2001, and issuing as U.S. Pat. No. 7,682,669B1 on Mar. 23, 2010, which is incorporated by reference as if fully setforth, including any figures, herein.

BACKGROUND OF THE INVENTION

This invention relates generally to coatings having an anti-thrombogenicmaterial immobilized thereon a surface area of various medical devicesin order to prevent acute thrombogenesis, and is particularly usefulwhen applied to intravascular stents. It is recognized that the presentinvention is not limited to intravascular stents and rather may be usedon various other medical devices where the same principles areapplicable.

Stents are implanted within vessels in an effort to maintain the patencythereof by preventing collapse and/or impeding restenosis. Implantationof a stent is typically accomplished by mounting the stent on theexpandable portion of a balloon catheter, maneuvering the catheterthrough the vasculature so as to position the stent at the treatmentsite within the body lumen, and inflating the balloon to expand thestent to engage the lumen wall. The stent plastically deforms into anexpanded configuration allowing the balloon to be deflated and thecatheter to be removed to complete the implantation procedure. The useof self-expanding stents obviates the need for a balloon deliverydevice. Instead, a constraining sheath that is initially fitted aboutthe stent is simply retracted once the stent is in position adjacent thetreatment site.

A significant concern associated with the implantation of a stent withinthe vasculature is the potential for restenosis and thrombogenesis whichmay in fact be exacerbated by the presence of the stent. The pressureexerted by the stent on the vessel wall may increase the trauma thatinduces hyperplasia and the presence of the stent in the blood streammay induce a local or even systemic activation of the patient'shemostasis coagulation system. Bound proteins of blood plasma,principally the adhesive proteins such as albumin, fibronectin,fibrinogen and fibrin, are known to trigger coagulation. The result istypically the adhesion and aggregation of thrombocytes on the surface ofthe stent. These proteins include peptide structures, e.g. theRGD-peptides composed of amino acids, such as glycine, arginine andasparagine. The same structures are involved in the adhesion ofthrombocytes as a consequence of receptors of the thrombocyte surface,e.g. collagen, von WilleBrand factor and fibrin interactions. The sameresult may arise with other biomaterials, generally of metal or plasticcomposition, which are inserted temporarily or implanted permanently inthe patient. The deposit of blood clots on the surface of thebiomaterial can result from a complex reaction of plasmatic and cellularmechanisms of coagulation that enhance and influence each other. Thus,the implantation of a stent to keep the lumen of the artery open mayonly hasten re-occlusion by promoting localized blood clotting andreactive inflammation. Indeed, studies indicate that stents and otheruntreated biomaterials can be covered with a relatively thick thrombusformation only minutes after contact with blood.

Various pharmacological agents have heretofore been used to address theproblem both on a systemic as well as localized level. The latterapproach is most often preferred and it has been found convenient toutilize the implanted stent for such purpose wherein the stent servesboth as a support for the lumen wall as well as a delivery vehicle forthe pharmacological agent. However, the metallic materials typicallyemployed in the construction of stents in order to satisfy themechanical strength requirements are not generally capable of carryingand releasing drugs. On the other hand, while various polymers are knownthat are quite capable of carrying and releasing drugs, they generallydo not have the requisite strength characteristics. Moreover, thestructural and mechanical capabilities of a polymer may be significantlyreduced as such polymer is loaded with a drug. A previously devisedsolution to such dilemma has therefore been the coating of a stent'smetallic structure with a drug carrying polymer material in order toprovide a stent capable of both supporting adequate mechanical loads aswell as carrying and delivering drugs.

Various pharmacological agents have previously been employed to reduceor suppress thrombogenesis and various methods have been developed toload such pharmacological agents onto a stent in order to achieve thedesired therapeutic effect. However, further improvement is desired bothin terms of the anti-thrombogenic efficacy of materials that can becoated onto stents as well as the methods by which such materials arecoated onto the stent. The present invention satisfies these and otherneeds.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings of the prior artmethods for imparting anti-thrombogenic characteristics to animplantable medical device, such as a stent, and more particularlyprovides new methods for covalently immobilizing an anti-thrombogenicmaterial, such as heparin in one of its various chemical forms, within apolymerized base coat layer posited on a surface of the stent. Heparinhas been proven to be resistant to thrombosis when used on the surfaceof an implantable medical device. The immobilization of heparin ondifferent material surfaces, particularly on metal, has for some timepresented significant challenges to stent manufacturers. This has beenthe case because of the highly hydrophilic nature of unmodified heparinwhich results in the coating being quickly washed away in thebloodstream. Heparin that is ionically bound converts heparin to alipophilic complex. Coatings having ionically bound heparin or a mixtureof ionically bound heparin and polymer increase the retention of heparinon the device surface. This is a somewhat limited improvement as withinhours, most heparin will be lost. The covalent attachment of heparin tothe device surface, however, tends to withstand a longer time challengein the blood. As set forth in the present invention, new methods forcovalently immobilizing heparin within the polymerized base coat layerposited on the device surface are advantageous in that such methods willhelp to eliminate SAT and significantly lower the restenosis rate. Theresulting stent is deployed at the treatment site to simultaneouslyprovide mechanical support to the lumen wall as well as to reduce theoccurrence of thrombogenesis.

In one embodiment, a base coat is applied to the surface of the deviceand the anti-thrombogenic material is immobilized thereon through aSchiff base reaction. The term “immobilize” as used herein refers to theattachment of the anti-thrombogenic material directly to a supportmember through at least one intermediate component. A general base coatmixture used in accordance with the present invention includes a bindingmaterial, a grafting material, a photoinitiator, and a solvent.Polymerization of the grafting material is carried out by irradiatingthe base coated device with ultra-violet (UV) light. The bindingmaterial of the base coat layer and the anti-thrombogenic materialimmobilized thereon have chemically functional groups capable of bindingto one another in order for the anti-thrombogenic material to besecurely bound to the medical device. Immobilization of heparin isachieved by reacting an aqueous heparin solution with a chemicallyfunctional group, such as an aldehyde compound, of the base coat layeron the surface of the medical device for an extended period of time.

In another embodiment, immobilization of the anti-thrombogenic materialoccurs through end-binding heparin in a Schiff base reaction on thesurface of the medical device. Specifically, this is achieved byreacting amine-terminated heparin with chemically functional groups ofthe base coat layer for an extended period of time. Alternatively,heparin is immobilized on the surface of the medical device with spacergroups. Following polymerization of the grafting material of the basecoat layer, amine-terminated polyethylene glycol is first reacted withchemically functional groups of the base coat layer, rinsed with water,and then reacted with unfractionated heparin and a water-solublecarbodiimide to form an amide linkage for the immobilization of heparinwith spacer groups. Another alternative embodiment includes theimmobilization of a mixed population of polyethylene glycol and heparinonto the device surface. Using the standard cinnamaldehyde base coat,the medical device is then immersed into a coupling solution of heparinand polyethylene glycol at various concentrations to react with thechemically functional groups of the base coat layer for an extendedperiod of time.

In other embodiments of the present invention, immobilization of heparinto the base coat layer is achieved by adding a surfactant bound heparinto the base coat. An amine group on the heparin chain may react and thenbind to the aldehyde group from cinnamaldehyde to allow for the completeimmobilization of the anti-thrombogenic material. Further, the use ofcarbodiimide chemistry to graft a specific chemical compound to theheparin chain can be employed to achieve immobilization of thecarbodiimide-reacted anti-thrombogenic material there to the base coatlayer of the medical device.

These and other features and advantages of the invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, thefeatures of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a coated stent of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along lines 2-2 of FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coated medical device of the present invention serves to support thewalls of a body lumen while preventing the formation of thrombi thereon.The present invention is not limited to any particular stentconfiguration or delivery method nor is the construction of the stentstructure limited to the use of any particular construction material.For illustration purposes, the following exemplary embodiments arelimited to intraluminal stents. However, it is recognized that thepresent invention is not limited to such applications and rather may beused on various other medical devices where the same principles areapplicable.

FIG. 1 generally illustrates a coated stent 12 of the present invention.The particular stent shown is for illustrative purposes only asvirtually any stent configuration can be coated in accordance with thepresent invention. In fact, the coating can be applied to any device tobe implanted or introduced into the body. The coating does not interferewith the stent structure or construction in any way and does not affectits deployment. All known stent designs with attendant delivery systemscan benefit from the coating of the present invention.

FIG. 2 is an enlarged cross-sectional view of a portion of the stentshown in FIG. 1 and illustrates a base coat layer 16 applied to thestent with the anti-thrombogenic material 18 immobilized thereon inaccordance with the present invention. The letter “A” represents theimmobilization of the anti-thrombogenic material into the base coatlayer of the medical device. The base coat layer 16 is applied directlyto all of the stent surfaces 14 including all of its edges. The basecoat layer 16 is formed from the polymerization of a base coat mixturewhich includes a binding material, a grafting material, aphotoinitiator, and a solvent. The binding material of the base coatlayer 16 and the anti-thrombogenic material 18 (e.g., heparin)immobilized thereon have chemically functional groups capable of bindingto one another so that the anti-thrombogenic material will be securelybound to the medical device through the immobilization of covalentlybound heparin to the binding material. Heparin is just one example of ananti-thrombogenic material that can be immobilized or coupled onto thesurface of the medical device as other glycosaminoglycans such aschondroitin sulfate, dermatan sulfate, and hyaluronate can also beimmobilized onto the surface using the same or similar chemistry as setforth below. The term “immobilize” as used herein refers to theattachment of the anti-thrombogenic material directly to a supportmember through at least one intermediate component.

In one embodiment, the binding material of the base coat is selectedfrom the group consisting of polyzairidine resin compounds,polycarbo-diimide resin compounds, aldehyde compounds, oxiranecompounds, acetoacetoxy compounds, and isocyanate compounds. The bindingmaterial of the base coat is used to strongly bind to both theanti-thrombogenic material and the grafting material. Preferredpolyzairidine compounds used in the present invention includetri-aziridine oligomer, such as Zenaca cs-100™ available from ZenecaResins. Exemplary of the carbodiimide compounds are XL-29SE™ availablefrom Union Carbide. Exemplary of the aldehyde compounds areglutaraldehyde, cinnamaldehyde, and acrolein. Exemplary of the oxiranecompounds are glycidyl methacrylate. Exemplary of the acetoacetoxycompounds are acetoacetoxy ethyl methacrylate. Exemplary of theisocyanate compounds are an aliphatic or aromatic isocyanate monomer,biuret or isocyanurate oligomer, isocyanato ethyl methacrylate or allylisocyanate, or polyol or polyamine chain extended variant of suchstarting materials as 1,6 hexamethylene diisocyanate, isophoronediisocyanate, toluene diisocyanate, diphenylmethane-diisocyanate, orbis(4-isocyanato cyclohexyl)methane. In addition, the isocyanatecompound can be the monomer or polymer made from allyl isocyanate orother such monomers.

The grafting material of the base coat 16 is selected from the groupconsisting of vinyl compounds, acrylate compounds, and allyl compounds,such as any oligomer or monomer with one or more vinyl, acrylate orallyl double bonds. The grafting material is used to graft to the devicesurface and cross-link with the binding material to form the base coatlayer. Preferred vinyl compounds used in the present invention includedi-vinyl benzene, n-vinyl pyrrolidone, and triethylene glycol divinylether. Exemplary of the acrylate compounds are tri-methylol propanetri-acrylate, pentaerythritol tetra-acrylate, and Bisphenol A.ethoxylate diacrylate. Exemplary of the allyl compounds are allyl ether,di-allyl maleate, and tri-allyl isocyanurate.

An example of a general base coat mixture which forms the base coatlayer, as shown in FIG. 2, after polymerization of the grafting materialon to the device surface, consists of the following chemical compounds,each listed with its respective weight in grams (g), used in accordancewith the present invention:

Urethane-acrylate (available from Cognis 6892 ™, 0.01-1.20 g formerlyHenkel 12-892 ™ or equivalent) Heterodifunctional monomer 0.10-1.20 gBenzophenone 0.001-0.5 g Hydroxycyclohexyl phenyl ketone 0.001-0.5 gCellulose acetate butyrate 0.00-1.00 g Ethyl acetate  3.00-200 g n-butylacetate  3.00-200 gThe heterodifunctional monomers that may be used in accordance with theinvention include, but are not limited to, cinnamaldehyde (aldehydebinding), glycidyl methacrylate (oxirane binding), acetoacetoxy ethylmethacrylate (acetoacetoxy binding), isocyanato ethyl methacrylate orallyl isocyanate (isocyanate binding).

With continued reference to FIGS. 1 and 2, the method for immobilizingthe anti-thrombogenic material 18, such as heparin in one of its variousforms (e.g., amine-terminated heparin, unfractionated or N-partiallydesulfated heparin), into a coating posited on the surface of themedical device of the present invention comprises, applying to themedical device a base coat mixture formed from a binding material, agrafting material, a photoinitiator, and a solvent, and polymerizing thegrafting material to enable the grafting material to graft to the deviceand cross-link with the binding material to form the base coat layer 16.The device coated with the base coat layer 16 is typically dried, eitherat room temperature or elevated temperatures, to enable for theevaporation of the base coat solution solvent. Many suitable solventsmay be used in the base coat mixture, including but not limited towater, alcohols, and ketones. Preferred common solvents used in themixture of the base coat include ester solvents, such as ethyl acetateand butyl acetate, and ketones, such as MEK and MIBK. Aromatics andglycol ethers may also be used as common solvents.

Polymerization of the grafting material is performed by irradiating thedevice coated with the base coat layer with ultra-violet (UV) light forapproximately eight to ten minutes. The process of UV cross-linking orcuring is well known in the art and can be executed by a number ofvarious methods. One type of UV source that can be used includes mediumpressure mercury bulbs. With the use of UV light, it is essential thatphotoinitiators be present in the base coat mixture. Photoinitiators arechemicals that absorb UV light energy and produce free radicals whichcause a chemical chain reaction for curing. Upon exposure to UV light ofthe correct wavelength, the photoinitiator is converted to an unstablefree radical. This radical will quickly react with chemically functionalgroups of the base coat mixture to enable the grafting material to graftto the device and cross-link with the binding material. Specifically,during the irradiation process, the acrylate, vinyl or allyl compoundsof the grafting material, cross-link to the functional groups of thebinding material, i.e., polyaziridine resin, polycarbodiimide resin,aldehyde, oxirane, acetoacetoxy, and isocyanate compounds. The result isa sufficiently adhered base coat layer which contains free unreactedbinding component functional groups on the surface of the coatingavailable to immobilize the anti-thrombogenic material (i.e., heparin)thereon. Preferred photoinitiators used in the base coat of the presentinvention include benzophenone, benzoin methyl ether, 2,2dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, andethyl 4-(dimethylamino)benzoate.

In another embodiment of the present invention, following polymerizationof the grafting material from the base coat layer as set forth above,the anti-thrombogenic material is immobilized on the device surface in aSchiff base reaction. Specifically, an aqueous heparin solution ofeither unfractionated or N-partially desulfated heparin is reacted withthe aldehyde groups of the base coat layer for approximately eighteen totwenty-four hours at a temperature in the range of 15° C. to 80° C. andabout pH 7.0. At the end of this reaction, the heparin solution iscompletely immobilized into the base coat layer of the device.

In another embodiment, subsequent to the polymerization of the graftingmaterial from the base coat layer by the same procedure set forth above,the anti-thrombogenic material is end-immobilized in a Schiff basereaction with the chemically functional groups of the base coat layer.The term “end-immobilized” as used herein refers to the attachment ofthe amine groups on the end of the heparin chain directly to a supportmember through at least one intermediate component. Specifically, theend immobilization of heparin is achieved by reacting amine-terminatedheparin, available from Celsus Lab, with the aldehyde groups of the basecoat layer for approximately eighteen to twenty-four hours at atemperature in the range of 15° C. to 80° C. and about pH 7.0. As aresult, heparin is completely immobilized into the base coat layer ofthe device.

In yet another embodiment, following polymerization of the graftingmaterial from the base coat layer as set forth above, the chemicallyfunctional groups of the base coat layer are reacted with excessamine-terminated polyethylene glycol (PEG), i.e., PEG(NH₂)₂ (Fluka#14499) having molecular weight (MW) 3400, for approximately eighteen totwenty-four hours at a temperature in the range of 15° C. to 80° C. andabout pH 7.0. Other molecular weights of PEG can be used including thosein the range of MW 500 to 10,000 (unavailable as standard catalogitems). The concentration of PEG(NH₂)₂ can range from about 0.01 mg/mlto 20 mg/ml. Immediately after the reaction, the base coat layer isrinsed with distilled water. Thereafter, unfractionated heparin isreacted on the device surface with amine-terminated PEG, i.e.,PEG(NH₂)₂, through carbodiimide chemistry to form an amide linkage. Awater-soluble carbodiimide, i.e.,1-(3-dimethyl-aminopropyl-3-ethylcarbodiimide) with a concentration ofabout 4.0 to 8.0 mg/ml, may be used at a pH of about 4.5 to 7.5 for twoto six hours at about room temperature. Subsequent to both reactions,heparin is completely immobilized into the base coat layer of thedevice. Other chemicals functioning similar to PEG that can be asubstitute for include hyaluronic acid, polyvinyl pyrrolidone (PVP) andother hydrogel type materials.

In another embodiment, subsequent to polymerization of the graftingmaterial from the base coat layer (using standard cinnamaldehyde basecoat) as set forth above, the chemically functional groups of the basecoat layer are reacted with a coupling solution of heparin and alphahydroxy, beta amino-Poly(ethylene glycol) [OH-PEG-NH₂] (Shearwater#2V3F0F02) having a concentration of about 0.01 mg/ml to 20 mg/ml. Thereaction between the base coat layer and the coupling solution can occurat all possible ratios of PEG to heparin (e.g., from 0% PEG, 100%heparin to 100% PEG, 0% heparin) for about eighteen to twenty-four hoursat a temperature in the range of 15° C. to 80° C. and about pH 8.0.Preferably, the coupling of PEG and heparin to the device surface isreacted at a temperature of about 55° C. A mixed population of PEG andheparin is completely immobilized to the device surface following theabove reaction.

In another embodiment, a surfactant bound heparin, such as benzalkoniumheparin or TDMA-heparin, is added to the base coat mixture. An aminegroup on the heparin chain reacts and binds to the aldehyde group ofcinnamaldehyde. The reaction between the surfactant bound heparin andthe binding material of the base coat runs for about eighteen totwenty-four hours at a temperature in the range of 15° C. to 80° C. andabout pH 7.0. Additionally, the base coat mixture can be preparedwithout a monomer through the use of free unreacted acrylate groups onthe device surface.

In another alternative embodiment of the present invention, Superoxidedismutase mimetic (SODm) (available from MetaPhor Pharmaceuticals) canbe grafted to the base coat with heparin to provide a covalentlyattached mixed population of heparin and SODm. SODm catalyticallyeliminates the superoxide anion radical, reducing oxidative stress.Accordingly, a synergistic effect with heparin can be achieved. Thegeneral base coat mixture set forth above using cinnamaldehyde as theheterodifunctional monomer is applied to the device surface by sprayingand cured by using medium pressure mercury bulbs for about eight to tenminutes. The device is then immersed in an aqueous solution of heparin(Sigma H-9266) at 7 mg/ml and SODm at 1 mg/ml, adjusted to pH of about8.0. The coupling reaction is carried out at a temperature in the rangeof 15° C. to 80° C. for approximately twenty hours. Subsequently, thedevice surface is rinsed in distilled water and immersed in an 8 mMsolution of sodium cyanoborohydride (Aldrich) in pH 7.0 phosphate bufferfor approximately twenty-four hours at room temperature. This secondreaction reduces the Schiff base to a more stable secondary aminelinkage. Thus, a grafted mixed population of SODm and heparin isachieved.

The alternative embodiment in the foregoing involving the covalentattachment of a mixed population of heparin and SODm is furtherillustrated by the following example. The general base coat mixtureusing cinnamaldehyde as the heterodifunctional monomer is applied to thedevice surface and cured by medium pressure mercury bulbs for abouteight to ten minutes. The device is then immersed in an aqueous solutionof heparin (Sigma H-9266) at 7 mg/ml and SODm at 1 mg/ml, adjusted to pHof about 8.0. The coupling reaction is carried out at a temperature inthe range of 15° C. to 80° C. for approximately twenty hours. Theheparin coupled device is then rinsed with distilled water and immersedin 8 mM sodium cyanoborohydride in pH 7.0 phosphate buffer forapproximately twenty-four hours at room temperature to reduce the Schiffbase. An EDC [1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide HCl]mediated coupling between carboxyl groups on heparin and the primaryamine group of SODm to yield an amide linkage is executed as follows.Separate solutions of 1 mg/ml SODm in 0.1M MES [4-morpholineethanesulfonic acid monohydrate]/KOH buffer, pH 7.0, and an 8 mg/ml EDCsolution in 0.1M MES/KOH buffer, pH 7.0, are prepared. Equal volumes ofthe SODm and EDC solutions are mixed and the heparin coupled device isthen immersed for approximately four hours at room temperature. Afterthe reaction, the device surface is rinsed with distilled water.

One method of coating the device with the base coat mixture is by spraycoating. However, the device may be coated by various alternativemethods, including but not limited to, dip coating at a given rate, wipecoating, or other suitable techniques known in the art.

In one of the embodiments, the device is an intraluminal stent. As setforth above, however, the present invention is not limited to anyparticular stent configuration or delivery method. Generally, thesurface of the device is cleaned prior to coating, and, althoughoptional, may also be plasma treated in order to improve coatingadhesion. Alternatively, a primer coat can be optionally applied to thedevice surface prior to the application of the base coat layer toimprove adhesion of the base coat. Exemplary of the primers that can beused include parylene, primacor (a copolymer of ethylene and acrylicacid), and EVAL™ (a copolymer of ethylene and vinyl alcohol).

As shown in FIGS. 1 and 2 of the presently preferred embodiment, thebase coat layer 16 is applied to the entire surface of the intraluminalstent. The coating, 30 however, may be applied to less than the entireouter surface of the stent.

While a particular form of the invention has been illustrated anddescribed, it will also be apparent to those skilled in the art thatvarious modifications can be made without departing from the scope ofthe invention. Accordingly, it is not intended that the invention belimited except by the appended claims. The following examples furtherillustrate the present invention. Other biological agents in addition toTDMA-heparin and BAC-heparin as mentioned in the examples below can alsobe incorporated into the base coat.

EXAMPLE 1

This example illustrates the immobilization of an anti-thrombogenicmaterial (e.g., TDMA-heparin) onto a support member of the presentinvention. A base coat formulation consisting of the following chemicalswere added into 15 ml toluene: 0.22 grams (g) oftridodecylmethlyarnmonium-heparin (TDMA-heparin), 1 g of Henkel 12-892urethane-acrylate, 0.08 g of benzophenone, and 0.08 g ofhydroxycyclohexyl phenyl ketone. Electrically polished 5 mm×25 mmstainless steel (SS) coupons were immersed into the solution. Afterair-drying for thirty minutes, the coupons were UV cured for eightminutes. One coupon was then dipped into 0.01% toluidine blue and rinsedwith excess water. The color of the coupon turned light purple,indicating the existence of heparin. The heparin impregnated coupon wasimmersed into 2 ml of reconstituted bovine plasma and included anexchange of plasma every twenty-four hours. After a time period offorty-eight hours, no color was detected in the toluidine blue assay,indicating most heparin was eluted from the coating. The control couponcoated with the above formulation, except without TDMA-heparin, showedno color change in the toluidine blue assay.

EXAMPLE 2

This example illustrates the immobilization of an anti-thrombogenicmaterial (e.g., benzalkonium-heparin) onto a support member of thepresent invention. A base coat formulation of the following chemicalswere added into 15 ml AMS (1665-Q, Techspray Inc., TX): 0.22 g ofbenzalkonium-heparin, 1 g of Henkel 12-892 urethane-acrylate, 0.08 g ofbenzophenone, and 0.08 g of hydroxycyclohexyl phenyl ketone.Electrically polished 5 mm×25 mm SS coupons were immersed into thesolution. After air-drying for thirty minutes, the coupons were UV curedfor eight minutes. A coupon was then dipped into 0.01% toluidine blueand rinsed with excess water. The color of the coupon turned lightpurple, indicating the existence of heparin. The heparin impregnatedcoupon was immersed into 2 ml of reconstituted bovine plasma andincluded an exchange of plasma every twenty-four hours. After a timeperiod of forty-eight hours, no color was detected in the toluidine blueassay, indicating most heparin was eluted from the coating.

EXAMPLE 3

This example illustrates the present invention using the base coatformulations from examples 1 and 2 to immobilize the anti-thrombogenicmaterial (e.g., TDMA-heparin and BAC-heparin) onto a support member.Each of the base coat formulations from examples 1 and 2 were added with1 g of cinnamaldehyde. Electrically polished 5 mm×25 mm SS coupons werecoated in the solution and then UV cured as above. Next, 0.2 g ofheparin (Sigma H-9266, ovine intestinal mucosa) was dissolved into 30 mlof distilled water. The pH of the solution was adjusted to 8.0 by adding0.1 N KOH. The Schiff base coupling reaction was carried out at 55° C.for eighteen hours. An elution study was performed in bovine plasmasimilar to examples 1 and 2 above. The toluidine blue assay wasperformed at different time points. The table below summarizes theresults:

Color at Color at Color at Coating t = 0 t = 24 hr t = 72 hr PU-acrylatecoated SS coupon Silver Silver Example 1, TDMA-heparin Light PurpleSilver embedded Example 2, BAC-heparin Light Purple Silver embeddedExample 3, TDMA-heparin Lighter Blue Same as t = 0 Lighter embedded +heparin coupling than t = 0 on surface Example 3, BAC-heparin Blue Sameas t = 0 Lighter embedded + heparin than t = 0 coupling on surface

EXAMPLE 4

This example illustrates the present invention by including a pegylationstep prior to the immobilization of the anti-thrombogenic material(e.g., heparin) onto the device surface. A base coat formulation of thefollowing chemicals were added together: 1 g of urethane-acrylate(Cognis 6892), 1 g (0.10-1.20 g) of a heterodi-functional monomer, 0.08g of benzophenone, 0.08 g of hydroxycyclohexyl phenyl ketone, 0.20 g ofcellulose acetate butyrate, 15 g of ethyl acetate, and 3 g of n-butylacetate. The SS coupons were coated with the base coat formulation andthen UV cured as above. The SS coupons were put into 1 ml of 4 mg/ml ofPEG(NH₂)₂ with a pH of 8.5 (MW=3400 from Shearwater Polymer) at 55° C.for twenty hours. After the Schiff base reaction, the coupons wererinsed with water.

An 8 mg/ml heparin solution (Sigma H-9266, ovine intestinal mucosa) and8 mg/ml EDC were prepared in pH=4 buffer. Next, 900 u/1 of heparinsolution and 900 u/1 of EDC solution were added into a vial containingthe pegylated coupon and reacted at room temperature for three hours.The coupons were then rinsed with water and dried. The heparin retentionexperiment was carried out by immersing the coated coupons intophosphorous buffer (pH=7.4) over an extended period of time (pleaserefer to table below for time points). An anti-thrombin III (AT-III)binding assay was performed to access heparin activity on the surface.The table below summarizes the results:

Average Heparin % Activity Sample Activity, U/cm² Remained Pegylatedcoupon, t = 0 0.15 PU base coat + PEG + Heparin, t = 0 0.26 100% PU basecoat + PEG + Heparin, t = 24 hr 0.15 58% PU base coat + PEG + Heparin, t= 94 hr 0.09 35%The heparin reaction performed with or without the pegylation stepworked, but the coupling efficiency was not significant. The couplingefficiency was improved by using N-desulfated heparin (available fromCelsus Laboratory).

EXAMPLE 5

This example illustrates the present invention using the base coatformulation from example 4 wherein the PEGylated support member wasreacted with an EDC and heparin solution. A solution was preparedcontaining 0.5 mg/ml of polyethylenimine (Aldrich) and 0.5 mg/ml ofNaCNBH3 in a pH=4 buffer and further adjusted the pH to 6.7. Thesolution was added into a 2 ml vial containing an ACS Multilink TriStar™(manufactured by Advanced Cardiovascular Systems, Inc., Santa Clara,Calif.) stent and reacted for seventeen hours at 55° C. The stent wassubsequently rinsed with distilled water.

An 8 mg/ml heparin solution (Sigma H-9266, ovine intestinal mucosa) and8 mg/ml EDC were prepared in pH=4 buffer. Next, 900 u/l of heparinsolution and 900 u/l of EDC solution were added into a vial containingthe pegylated coupon and reacted at room temperature for four hours. Thecoupons were then rinsed with water and dried. The heparin retentionexperiment was carried out by immersing the coated coupons intophosphorous buffer (pH=7.4) for an extended period of time. An elutionstudy produced results similar to those in example 4. The coated stentwas e-beam sterilized at a dose of 50 kGy. An AT-III binding assay wasperformed to access heparin activity on the surface. The table belowsummarizes the results:

Time Point & Sterilization AT-III Binding (units/stent) No E-Beam, t = 00.4 After E-Beam, t = 0 0.39 No E-Beam, t = 24 hrs in saline 0.2 AfterE-Beam, t = 24 hrs in saline 0.28

1. A method for immobilizing an anti-thrombogenic material onto acoating deposited on a surface of an implantable medical device, themethod comprising: preparing a base coat mixture for application to thesurface of the medical device, the surface of the implantable medicaldevice optionally coated with a primer layer; applying the base coatmixture to the surface of the medical device; polymerizing the base coatmixture to form a base coat layer on the medical device, the base coatlayer comprising chemically functional groups; performing a reactionbetween the chemically functional groups of the base coat layer andexcess amine-terminated material; rinsing the base coat layer withwater; and performing a reaction between the anti-thrombogenic materialand amine-terminated material on the surface of the medical device;wherein the amine-terminated material is amine-terminated hyaluronicacid or amine-terminated polyvinyl pyrrolidone.
 2. The method of claim1, wherein the reaction between the excess amine-terminated material andthe chemically functional groups within the base coat layer runs forabout eighteen to twenty-four hours at a temperature in the range of 15°C. to 80° C. and about pH 7.0.
 3. The method of claim 2, wherein theexcess amine-terminated material is amine-terminated polyvinylpyrrolidone.
 4. The method of claim 3, wherein the concentration of theamine-terminated material is about 0.01 mg/ml to 20 mg/ml.
 5. The methodof claim 1, wherein the anti-thrombogenic material is unfractionatedheparin.
 6. The method of claim 5, wherein unfractionated heparin isreacted with amine terminated material and a water-soluble carbodiimideon the surface of the medical device for the immobilization of heparinthereon.
 7. The method of claim 6, wherein the reaction betweenunfractionated heparin and amine-terminated material with the watersoluble carbodiimide on the surface of the medical device runs for abouttwo to six hours at about room temperature and about pH 4.5 to 7.5. 8.The method of claim 1, wherein the anti-thrombogenic material isN-desulfated heparin.
 9. The method of claim 8, wherein N-desulfatedheparin is reacted with amine terminated material and a water-solublecarbodiimide on the surface of the medical device for the immobilizationof heparin thereon.
 10. The method of claim 9, wherein the reactionbetween N-desulfated heparin and amine-terminated material with thewater soluble carbodiimide on the surface of the medical device runs forabout two to six hours at about room temperature and about pH 4.5 to7.5.
 11. An implantable medical device comprising a coating deposited ona surface of the implantable medical device, the coating comprising ananti-thrombogenic material attached to the coating by the method ofclaim
 1. 12. The method of claim 1, wherein the excess amine-terminatedmaterial is amine-terminated hyaluronic acid.